Coded track circuit signaling system



March 16, 1943.

T. J. JUDGE CODED TRACK CIRCUIT SIGNALING SYSTEM 3 Sheets-Sheet 1 Filed July 9, 1941 M100 OWN INVENTOR ATI'ODRNEY BYM -Mani! "r. J. JUDGE CODED TRACK CIRCUIT SIGNALING SYSTEM Filed July 9, 1941 3 Sheets-Sheet 2 kwm l bv rllll mut fi ig 3n A'ITORNEY 3 W I i; m M m n n M o mdmfifilfi $7 3 n m vn MM UTM A March 16, 1943. T. J. JUDGE comm) TRACK CIRCUIT SIGNALING SYSTEM Filed July 9, 1941 3 Sheets-Sheet 3 INZE7NTOR ATTdRNEY Patented Mar. 16, 1943 2,314,280 pm) TRACK CIRCUIT SIGNALING SYSTEM Thomas J. Judge, Rochester, N. Y., assigncr to General Railway Signal Company, Rochester,

Application July 9, 1941, Serial No. 401,607

22 Claims. (Cl. 246'33) The present invention relates to signaling systems of the absolute-permissive-block type and more particularly to a double or duplex coded track circuit for such systems, and is an improvement over the systems disclosed in the prior applications of Phinney, Ser. No. 362,636, filed October 24, 1940, now U. S. Patent 2,272,581 granted February 10, 1942, and Phinney et al., Ser. No. 370,186, filed December 14, 1940. By coded track circuit is mean-t a track circuit of the coded type wherein impulses of current are repeatedly applied to one end of the track circuit and suitable code responsive apparatus detects the code and its character at the other end of such track circuit. By duplex coded track circuit is meant a track circuit in which codes may be applied at both ends of the section of track and code responsive apparatus may be connected at both ends thereof, wherein each code responsive apparatus only responds to the code applied by the code applying apparatus at the other end of the section and wherein codes are received at both ends of said section substantially continuously. The term driven code is used to mean a code which is created by suitable code creating apparatus directly, that is, apparatus which originates the length of impulses and the time spacing between the impulses. By inverse code is meant a code which is inserted between the impulses of a driven code and usually originates at the opposite end of the track section. By inductive kick repeater relay is meant a relay which responds to an induced current. As shown, the induced current is derived from a winding of another relay TR into which it is induced.

In order to control a signal in accordance with traffic conditions in one or more blocks in ad'- vance, without the requirement of signal control line wires, it is desirable to have the track relay, or other code following apparatus, located at that end of the block which is adjacent the entering signal. Obviously, if trafilc moves in both directions, as is the case in single track railroads, there should be a signal at each end of such track section for governing traflic into the sec tion at that end, and consequently it becomes necessary, or at least desirable, to have a track relay, or code following means, at each end of the track section to avoid the need of special con trol line wires. Since traffic conditions in opposite directions from a particular tracksection may be different, it becomes apparent that the codes transmitted in opposite directions through the same track section may be different, insofar as the length of the impulses or their polarity is concerned or the durations of their spacing.

Also, when continuous inductive tram control is employed, "it 'is found necessary to apply the code to the exit end of a track section for the particular direction in which the train is moving, so that this code may be detected by suitable receiving apparatus mounted on the locomotive in front of the first axle thereof and in inductive relation to the track rails. In view of these facts it is desirable to employ a duplex track circuit, so to speak, in which a track relay or other code following means at each end of the track section controlled by energy applied to the opposite end of Such section is preferably employed.

In accordance with the present invention it is proposed to employ a duplex track circuit ar range'ment in which complete codes are alternately applied at opposite ends of a track section, each code of which is received and de-c'o'ded at the opposite end from that at which it was applied. Also the codes under consideration are of course driven codes, that the codes are created by special code creatin apparatus. In order to keep these code applying apparatuses in such synchronis'm that they are alternately applied at opposite ends of the track section without interference, it is proposed to employ a socalled inverse code which is applied s'oas 'to have its impulse occur between the impulses of the driven code, and so that each inverse code impulse controls the apparatus at the driven 'code end so that the driven code is discontinued shortly after the reception of an inverse code impulse; suitable time measuring apparatus being of course employed to determine the time when such inverse code shall be applied.

In one form of the invention an approach track relay is employed for preventing a socalled code fight after an occupied track circuit has become vacated, this approach series track rel'ay being of the usual ty'pe, n'amelya, series relay included in series with the track battery, this approach track relay in combination with slow dropping repeater relays rendering the driven c'o'de creating apparatus inoperative for a short period of time after each occupancy of the track circuit.

Other objects, purposes and characteristic features of the present invention will in part be described in the specification hereinafter and will in part be obvious from the accompanying drawings, in which:

Figs. 1A and 1B, when laid side by side, illustrate the apparatus applied to one block and to the entrance ends of two adjacent blocks of a preferred embodiment of the present invention; and

Fig. 2 illustrates a modified form of the present invention in which suitable apparatus to prevent a code fight is incorporated.

Structure, Fig. 1

Referring to Figs. 1A and 1B, laid side by side and left to right in that order, it will be observed that a railway track having rails I, divided by insulating joints 2, has been illustrated. The particular stretch of track illustrated includes a block N and the adjacent ends of two blocks M and 0. At each of these block junctions is provided a pair of opposite signals, namely, a signal for governing trafiic in each direction along the track and located at the same location. The signals for governing east-bound tratfic have been designated S6 and S8, whereas the signals for governing west-bound traffic have been designated S1 and S9. Although these signals may be of any suitable construction, such as semaphore signals, search-light signals, position light signals, or multiple aspect color light signals, for convenience only multiple aspect color light signals have been illustrated. At each end of the block N is provided a selecting relay FR which has contacts, such as Hi and H for the relay FRB, which relays determine or select whether code creating apparatus or code receiving apparatus shall be connected to the track rails at that end of the block. The driving code is applied by the code applying relay CPR, which in turn is controlled by one of the coders C illustrated. When the selecting relay FR is energized the track relay TR is through the back contact 22 of relay IKP included directly in the track circuit, whereas if this selecting relay FR is deenergized the coding contact, such as the contact I2 for the relay CPRE, is included in the track circuit. Each of the block ends is provided with a main or driven code battery B and with an inverse code battery BI, each of these reference characters B and BI being provided with a sufiix corresponding to the sufi x of the signal governing traflic into the section at that end. Each of the block ends is provided with an inverse code relay IR, which relay is connected to the track circuit when both the selecting relay FR and the code applying relay CPR assume their deenergized position. Each block end is also provided with a timing relay JR. This relay JR by its drop-away characteristic determines the time during which a driven code may be sent in a particular direction. These timing relays JR when deenergized connect an inductive kick repeater relay IKP in a circuit including an inducing winding of the track relay TR. This inductive kick repeater relay is picked up inductively by the next received driven code element and in turn causes an inverse code element to be sent during the next time space and to the then transmitting end. This inductive kick repeater relay IKP is a polar relay and responds only to current of one polarity and will respond only to current induced therein due to dying flux in the track relay core due to the next preceding code impulse. Also, if desired, a rectifier may be included in series with such relay to block the flow of all currents of another polarity. Since the apparatus illustrated constitutes a portion of an absolute-permissive-block signaling system the usual directional stick relay S has also been illustrated for each signal. Since decoding apparatus is well understood by those skilled in the art and since specific decoding apparatus has been illustrated in the application of Phinney et a1., Ser. No. 370,186, above referred to, the decoding track relay TP, the decoding home relay HR, and the decoding distance relay DR have been illustrated conventionally as being controlled by the intermittent operation of the contact I5 of the track relay TR. It may be pointed out that the decoding track relay TP is energized each time a code is received irrespective of whether it is a 75 impulse per minute code, a home code of impulses per minute, or a distant code of 240 impulses per minute, whereas the decoding relays HR and DR respond only to their respective codes of 120 impulses per minute and 240 impulses per minute, respectively.

Referring again to Fig. 1A, the inverse code relay IRS is provided with a contact I6 and a stick contact I1 and the timing relay JRB is provided with control contacts l8 and I9. The selecting relay FRG is provided with two transfer contacts I0 and H and with a control contact 20 The inductive kick repeater relay IKPB is provided with a control contact 22 The directional stick relay 58 is provided with control contacts 23 2 and 25 and with a stick contact 26 The decoder track relay TPG is provided with control contacts 28 and 29 the decoder home relay HRS is provided with control contacts 30 SW, 32 and ,33 and the decoder distant relay DRS is provided with control contacts 34 35 36 and 31 Only one set of coders C is provided for each pair of opposite signals. The signal location of signals S6 and S1 is provided with coders 1506-1, IZBCG-l and 248C6-1 having coding contacts 40 ll and 42 respectively. Since the control circuits and apparatus for each of the signals S5, S1, S8 and S9 is the same, like relays and like contacts for these Various signals have been designated by like reference characters having distinctive prefixes, suffixes and/ or exponents.

Operation of Fig. 1 system Let us first consider how a driven code is alternately applied at opposite ends of the block N assuming the absence of trains and clear traffic conditions on adjacent tracks in both directions from the block N. It will be observed that the selecting relay FRS is in its energized position, whereas the selecting relay FR9 is in its deenergized position. It is also readily seen that the selecting relay FRG is energized because its energizing circuit including the front contact I6 of the inverse track relay IE6 is closed, whereas, the corresponding contact I6 of the inverse track relay IR9 is open. It is also readily understood that the inverse code relay 1R6 is in its energized position because its stick circuit including its stick'contact I1 and the front contact it of the timing relay JR6 is closed; whereas -a similar stick circuit for the inverse code relay IRS! is open at its stick contact H although a similar front contact I 8 in its stick circuit is also closed. Attention is also directed to the fact that the timing relay JR at both ends of the block N assume their energized position even though the energizing circuit for the timing relay JRS is open (the energizing circuit for the timing relay JRS being closed). It may be pointed out at this time that although the timing relays JR are rather quick in picking but are exceedingly slow dropping, and will not drop until about three seconds have CPRQ. -intermittently energized at the 240 impulse per elapsed since their energizing circuits have been broken. With the apparatus in the condition i1- lustrated in Figs. 1A and 13, a driven code is transmitted from the east end or right-hand end of the block N, this code originating insofar as its presence in the track circuit is concerned at the coding contact I2 of the code applying relay This code applying relay CPR9 is now minute rate through a circuit which may be traced from the terminal plus of a suitable source of current, through front contact 42 of the coder 240C39, front contact 34 of the decoding distant relay DB8, back contact 30 of the decoding home relay HRS, front contact 28 of the decoding track relay TF8, through back contacts 25 and 23 of the directional stick relays 8S and 9S, respectively, through the winding of the code applying relay CPR9, to the other terminal minus of the same source of current. The intermittent picking up of the code applying relay CPR9 at the 240 impulse per minute rate causes the track battery B9 to be applied to the track rails to cause current flow through the track rails at the rate of 240 impulses per minute. This code of 240 impulses per minute is, during unoccupied conditions of the block N, applied to the lower winding of the track relay TR6 at the west end of the block N. The intermittent picking up of the contact I5 of the track relay TRt associated with the signal S6 at the 240 impulse per minute rate causes the decoder relays TPS and DES to continuously assume their energized position, whereas the decoder relay HRS remains in its retracted position. This results in the illumination of the green lamp G of the signal S6,v

front contact l8 included in the stick circuit for the inverse code track relay IRS to cause this relay IRS to assume its retracted position and open its front contact "5 included in the energizing circuit of the selecting relay FRii. Before the selecting relay FRB, however, has had time to drop, the upper winding of the track relay TR6, due to the falling current in its lower Winding,

induces a current in the winding of the inductive kick repeater relay IKPB. This induction of a current in the relay IKPt is possible because the back contact I9 of the relay JR6 is now closed. This induced current flowing in the winding of the relay IKPS will pick up this relay upon the termination of an impulse of the driven code only. The picking up of the inductive kick repeater relay IKPt causes an inverse code element to be transmitted from the inverse code battery BIB through a circuit including the front contact 22 of the inductive kick repeater relay IKPG, the front contacts IE and II of the selecting relay PR6 and including the back contacts I6 and l l of the selecting relay FEB located at the east end of the block N during an off period of the code applying relay CPRS (namely, at the time when the back contact I2 of the code applying relay CPR9 is closed) thereby causing the inverse track relay 1R9 to be picked up by the inverse code curthe inverse trackrelay lR't'of course causes this track relay 1R9 to pick up and since the front contact l8 of the selecting relay J39 in 'the'stick circuit for this inverse track relay IE9 is closed, the inverse track relay IRS will be stuck up through its stick circuit the very instant that its stick contact I1 closes. The picking up of the inverse track relay 1R9 will, of course, at its front contact I6 close the energizing circuit for the selecting relay FRS thereby disconnecting the east-end of the track circuit of th block N from the coding contact I2 and connecting this east end of the track circuit to the lower winding of the track relay TR9 through a branch circuit including back contact 22 of the inductive kick repeater relay IKPE. The apparatus at the east end of the block N, namely, the apparatus associated with the signal S9, is now ready to receive a driven code from the west end of this block N. Also, since the selecting relay FRB is a rather quick acting relay it opened its front contacts IQ and II and closed its back contacts H1 H and 29 very shortly after the relay IRE opened its front contact l5. Similarly since the selecting relay FRS is rather quick acting it will pick up very quickly after the inverse track relay IRE! closed its front contact Hi due to the reception of an inverse code element transmitted from the inverse code battery BIS. This dropping of the selecting relay PR6 connected the coding contact I2 included in series with the track battery B6 to the west end of the track circuit for the block N, so that the code applying relay CPRt may through the medium of its contact 12 apply a code to the West end of the block N in accordance with the particular coder 'lfiCfi-i, iZfiCii-l or 2MICET then connected to the code applying relay CPRS. Similarly the picking up of the selecting relay PR9 connects the lower winding of the track relay TRS to the east end of the track rails of block N to receive the code applied to the west end of this block by the coding contact l2 of relay CPRE. The dropping of the selecting relay F35 also results in the closure of its back.

ment has been transmitted from east towest over the rails of the block N. Also, this picking up of the timing relay JRt results in the closure of its front contact I8 Since, however, the inverse track relay IRS is now intermittently connected (by back contact I2 to the dead track rails of block N and since its stick contact ll is open (and remains open until an inverse code element is transmitted westwardly through the block N) the closure of this front contact I8 of th timing relay JR5 performs no particular function.

It will be readily understood that the timing relays JRt and JR9 for the block N both assume their energized position almost continuously, that is, one relay is in its attracted position because its energizing circuit is closed, and the other is in its attracted position because it has not yet dropped in response to the previous opening of its energizing circuit. The relays JRB and JR!) are slow to drop and quick to pick up and V will stay down, only momentarily because the energizing circuit of each is re-closed as soon as *the associated selecting relay FR controlled thereby has responded to the dropping of such relay JR. The decoding relays TP, HR and DR are slightly more slow dropping than the timing relays JR, because it is desirable to have the particular decoding relays which are energized in response to the received code to remain in their energized position until the timing relay JR at the opposite end of the block has assumed its retracted position and has caused a new driven code to be applied at the opposite end of the block. In other words, the structure is such that a driven code is transmitted from one end to the other end of the block for a period of about three seconds after which a driven code is transmitted from such other to said one end of the block and the decoding relays which are picked up by such code remain in their attracted position during the three second interval when no code is received. The apparatus is shown in its normal clear traffic condition with the green lamps G of each of the signals S5, S1, S8 and S9 energized.

Let us now assume that there is an east-bound train moving in the block M. The presence of the train in the block M of course causes continuous deenergization of the track relay TR'I; resulting in continuous deenergization of the decoding relays DR'I HR! and TPl. Since the directional stick relays 1S and 68 are in their normal retracted position, the relay is only picking up in response to the movement of a west-bound train by the signal S! and the relay (is picking up only in response to the movement of an east-bound train by the signal S5, it will be observed that the code applying relay CPRG is energized at the coding rate of '75 impulses per minute through a circuit including the control contact 49 the back contact 22 of the relay TPl, the back contact 2 1 of the directional stick relay is, and the back contact 23 of the directional stick relay S. A impulse per minute code is therefore transmitted from west to east through the block N, which causes the decoding relays DB9 and HRS to be deenergized and assume their retracted position, but allows the decoding track relay TF9 to remain in its energized attracted position Under this condition of the decoding relays associated with the signal se it is apparent that the red lamp R of the signal SE is energized through a circuit including the back contacts 33 and 3'i of the relays HRS and DR, respectively. In the same way as just explained a '75 impulse per minute code is transmitted from west to east through the block 0 the code applying relay CPRB being controlled through back contacts 36 and 34 of relays HR!) and DB9, respectively, instead of through back contact 28 of relay TP, so that the usual tumble down of danger signals is assured.

At the east end of the block M a code of 240 current impulses per minute rate is applied by the coding relay CPR'i. It should be noted that under normal clear trafiic conditions the coder 2 liCE'l is operated through a circuit including the front contact of relay DB6. This relay CPR? is energized 240 times per minute through a circuit including coding contact 62 front contact 34 of relay DRE, back contact 30 of relay HRE, front contact 28 of relay TPE and back contacts 24 and 23 of relays 3S and TS, respectively, control apparatus of the eastbound train in block M will therefore give a clear indication. The signal S6 of course indicates clear by reason of clear trafiic conditions ahead as has been assumed.

Let us now assume that the east-bound train under consideration accepts and passes the clear signal S6. This advance of the train into the block N causes the decoding track relay 'I'PS to assume its retracted position before the distant decoding relay DRE assumes its retracted position as a result of which the directional stick relay 68 has its pick-up circuit including the front contact 35 of the relay DB6 and the back contact 29 of the relay TPB closed at least momentarily. The directional stick relays are sufficiently slow dropping so that they will not drop during the movement of the contact 36 from the position in which it is included in the pick-up circuit to the position where it is included in the stick circuit for such stick relay. The directional stick relay 63 upon the dropping of the distant decoding relay DRS is therefore energized through a stick circuit including its own stick contact 26 and the back contacts 32 and 36 of the relays HRS and DR6, respectively, in series. With the directional stick relay 68 now energized the closure of its front contact 25 applies energy to the motor of the coder I2flC6-'I so that this coder delivers its code of impulses per minute. Also, with the directional stick relay (is now in its attracted position and with the directional stick relay IS in its retracted position the code applying relay CPR'I is intermittently energized at the 120 impulse per minute code rate, and as soon as the rear end of the train leaves the block M, this 120 impulse per minute code rate of current is applied to the east end of the block M through a circuit including coding contact di front contact 24 of stick relay 6S and back contact 23 of directional stick relay is, thereby causing the signal next in the rear of the signal SS toassume its caution indicating condition. The coder i2ilC5l is operated only if one of the stick relays BS or 78 assumes its energized position as, for instance, through front contact 2%: of either of these stick relays.

The entrance of the east-bound train into the block N, of course, results in the continuous deenergization of the track relays T36 and TRB at the two ends of the block N, so that all of the decoding relays TPS, HPtt, DRiS, DB9, HRS and TPB assume their retracted position.

Let us assume, for convenience, that the relays FEE, 1R6, JRE, FRS, IRS and JRii assume the positions illustrated in the drawings the moment the east-bound train entered the block N. It is, of course, readily seen that the code which was then applied by the code applying relay CPR9 at the east end of the block N could not reach the track relay TRS located at the west end of the block N because this coded track circuit current was shunted away by the Wheels and axles of the train under consideration. This is also true of the code impulses transmitted in an eastbound direction through the block N. After a short interval of time (about three seconds after its circuit was broken) the timing relay 'JRB will, of course, assume its retracted position and will close a circuit for the inductive kick repeater relay IKPQ. This will, however, be of no avail because there is no current change in the lower winding of the track relay TRB so that no current can be induced in the inductive kick repeater relay IKP6. For this reason, no inverse code is applied to the west end of the track circuit for the block N and even if such inverse code were applied it could not reach the relay IE9 at the east end of the block N, because of the presence of the east-bound train in the block N, which, of course, shunts such current applied to the track circuit at one end away from the Opposite end of such track circuit. In other words, the dropping of the timing relay JRB will merely result in the deenergization and dropping of the relays IRS and FRG. After a very short interval of time the timing relay JRB will again b picked up by reason of the closure of the back contact 26 of the relay FRB. The relays FR, IR and JR of both ends of the block N therefore assume like positions, that is, relays JR are energized and assume their energized positions and the relays FR and IR assume theirdeenergized positions. With the relay FRB now in its deenergized position the code applying relay CPRB will continue to apply code to the west end of the block N in accordance with traffic conditions in advance of the signal S1 in the same manner as code applying relay CPR9 applies a code to the east end of the block N in accordance with traffic conditions in advance of the signal S8.

At the east end of the block N no change in the positions of relays FR9, IRS and JRQ will take place because the inverse code element is not transmitted, which in the absence of the train would have been transmitted and would have picked up the inverse track relay IRS. Since this inverse code was not transmitted and therefore left the inverse track relay IRS deenergized and this left the selecting relay PR9 in its retracted position no change in the code transmitting apparatus at the east end of the block N took place. In other words, a code is applied ahead of the east-bound train in the block N in accordance with traffic conditions in advance of the signal S8 through the medium of the code applying relay CPR9 so that if suitable train control apparatus were present on the train the conditions of traffic could be continuously inductively detected in accordance with code current flowing in the track rails and indicated by suitable cab signals in the cab of such train. In the same way coded' current reflectin conditions of traffic in advance of the signal S! is applied to the west end of the block N so that traific conditions in advance of a west-bound train may also be visually indicated on the train.

Let us now assume that the east-bound train under consideration advances into the block 0. This, of course, results in the picking up of the directional stick relay 83, which relay SS is thereafter maintained energized through its stick circuit hertofore traced. Also, the picking up of the directional stick relay 8S with the directional stick relay 9S deenergized causes a code of 120 impulses per minute to be applied to the east end of the block N as soon as the rear end of the east-bound train has moved entirely out of the block N. 'As already pointed outa code is applied to the west end of the block N in accordance'with traffic conditions in advance of the signal S1. The simultaneous application of codes at opposite ends of the block N, as is now the case, may result in impulses being applied at'both ends ofthe block N at the same instant. Since, however, the batteries'Bfi and B9 are poled to oppose each other no particular harm is done because if these impulses are applied at exactly the same instant and remain applied'for exactly the same durations no current flow to any appre ciable extent results. Such a code fight, so to speak, can however not last very long because the coders would either be applying difierent codes which would bring them out of inverse synchronism, or if they happen to be applying the same code they would soon be out of step because the apparatuses would at best be slightly different in construction. Under the conditions assumed the inverse code relay IR at one end or the other of the block N would be picked up in response to the driven code applied to the opposite end of such block N the moment a slight change in phase relation between the operation of the relays CPR takes place, and thereafter the selecting relays FRS and FR! will be alternately energized and picked up for reasons already explained. It is, of course, readily understoood that the end at which the inverse track relay IR is picked up becomes the receiving end of the then applied driven code and that thereafter codes will be alternately applied to opposite ends of the block N for repeated three second intervals in a manner as heretofore described.

Reviewing now briefly the system illustrated in Figs. 1A and 13, this sytem is an absolute-permissive-block signaling system employing a track circuit of the duplex rocking type. The word duplex signifies that trafilc conditions are manifested at both ends of the track section by separate track circuits including separate track relays and the same track rails. The word rocking signifies that these track circuits are rendered available alternately at such a fast rate that the track relay and its associated decoding means of each track circuit substantially continuously manifests traflic conditions in that block and in blocks beyond the opposite end of such block. Th con-, struction of the system is such that during both occupancy and unoccupancy of a particular block codes of current impulses .are applied at both ends of the block, these codes being of a nature to manifest traffic conditions beyond that end. It is thus seen that for each direction of movement of a train through such block coded current will flow in the track rails ahead of the train coded in.

tending from the source end of the track circuit down one rail through the wheelsand axles of the train and back through the other rail. Since each of these coding circuits have currents therein coded in accordance with traffic conditions ahead of the train, cab signals controlled in accordance with the codes in these coding circuits as inductively detected will manifest in the cab traffic conditions ahead. When a block becomes unoccupied the relays FR and IR will assume their deenergized position and the relays JR will assume their energized position at both ends of the track circuit. If both of the code applying relays CPR operated in perfect synchronism opposing impulses of current would be applied at both endsof the track section resulting in zero current flow. Such synchronism can, however, not continue long, especially if the timing of the coders C at opposite ends of each section is slightly different. If desired, the coders at opposite ends of the same track section may be especially'timed to avoid such synchronous operation. After a short time of such synchronous operation of the code applying relays CPR one or the other of the inverse track relays IR will be picked up by the impulse applied at the opposite end of the track section. When this occurs the relays IR and FR at that end will continuously assume their energized position and their associated relay JR will be deenergized, but due to its slow dropping characteristic will not drop.

for a period of about three seconds, at which time it will drop to close its back contact I9 included in the circuit of the inductive kick relay IKP. During and following the next received impulse, the relay FR not yet having dropped in response to the dropping of the associated relay JR, an inverse code element is transmitted through front contact 22 of the relay IKP to the opposite end of the track section, and this inverse code impulse changes the apparatus at such opposite end from transmitting apparatus to receiving apparatus. It is thus seen that the apparatus at one end is changed from receiving apparatus to transmitting apparatus by dropping of the timing relay JR and that this results in the transmission of a single inverse code impulse to the opposite end of the track section which then picks up the inverse track relay IE to convert such opposite end from constituting a transmitting apparatus to constituting a receiving apparatus. In other words, synchronization of the apparatuses at opposite ends of a track section is accomplished by transmitting a synchronizing impulse through the same track rails which constitute a portion of each of the duplex track circuits.

Structure of Fig. 2

The apparatus illustrated in Fig. 2 of the draw ings is identical to the structure shown in Figs. 1A and 1B of the drawings insofar as the apparatus associated with the signal Sill is concerned, a portion of this structure having, however, been omitted for convenience. The structure associated with the signal SI I in Fig. 2 of the drawings, however, differs from the structure associated with the signal S9 of Fig. 1B of the drawings by the add tion of an approach track relay ATI I included in series with the ma n battery BII and by the addition of the front contact repeater relay AFPII and the back contact repeater relay ABPII controlled by this a proach track relay ATII and further by the addition of the control contacts 52 and 53 controlled thereby. It is readily seen that the front contact repeater relay AFPI I will p ck up and rema n in its energized position continuously during intermittent closure of front contact of the approach track relay AT" and that the back contact repeater relay ABPII wi l continuously assume its ener ized posit on in response to intermittent closure of back contact 50 of the approach track relav ATII provided that the front contact repeater relay AFPII is then assuming its ener ized position and maintains its front contact 5I closed.

It should be observed that back contact 53 of relay ABPI I and front contact 52 of relay AFPI I are included in multiple in the energizing circuit of the code applying relay CPRII. From the construct on illustrated it will be observed that the energizing circuit for relay CPRII will be open at contacts 5-2 and 53 only for a short time following each occupancy of the track section or block P, that is, following the instant of unoccupancy of such section. In other words, the apparatus at the east end of the track section extending from signal SIII to signal SII cannot transmit a code immediately after the track section P is vacated, whereas the apparatus at the west end can, the west end apparatus not including a series approach relay AT and associated relays controlled thereby. The relays AT, ABP and AFP may, therefore, be considered to be suppressing or lock-out apparatus to suppress the operation of the code applying apparatus at the east end of the block P for a time long enough to allow the code applying apparatus at the west end The apparatus illustrated in Fig. 2 functions in exactly the same way as does the apparatus illustrated in Figs. 1A and 13, except for a moment following the unoccupancy of the block P. As heretofore pointed out in connection with the operation of the system illustrated in Figs. 1A and 1B, a code is applied at both ends of the block P during occupancy of this block P. Since the approach track relay ATII is a series approach relay of the usual construction this relay ATII remains in its deenergized position even though it is intermittently weakly energized by the driven code which flows from the main battery BII. Thus the approach track relay ATI I is a marginal relay which will not be picked up under unoccupancy of the block P, but which will intermittently pick up during occupancy of the block P in response to the intermittent picking up of the code applying relay CPRI I. With the block P now occupied, as has just been assumed, the approach track relay ATI I is intermittently picked up in response to the impulses of the driven code which is derived from the battery BI I and which flows through this approach relay ATII to the track rails at the east end of the track circuit for block P. This intermittent picking u and dropping of the approach track relay ATII causes the slow dropping code'repeater relays AFPII and ABPII to both assume their energized position continuously as illustrated in Fig. 2 of the drawings. so that the front contact 52 of the relay AFPII is closed and the back contact 53 of the relay ABPI I is open. It is thus seen that the code applying relay CPRII ma be energized through the front c ntact 52 of the front approach coding relay AFPI I. Let us now assume that the train under consideration moves out of the block P and leaves this block P unoccupied. S nce the approach relay AT is only provided at the east end of the block P it is readily seen that the m vement of the train out of the block P causes different ac ion at one end than at the other end of the block P. in that the approach relay ATII assumes its retracted position continuous y as a result of wh ch the relays AFPII and ABPII are deenergized and dropped away in sequence in that order. It is also readily seen that the relay ABPI I will not start dropping unt l the relay AFPII has actually moved to its deener ized position from wh ch it becomes apparent that the front contact 52 of the relay AFPII opens before the back contact 53 of the relay ABPII closes. In other words, the code applying relay CPRII remains deenergized during the drop-away time of the approach track repeater relay ABPI I. Dur ng this time when the code applying relay CPRI I has its energizing circuit open the inverse track relay IRII is connected to the east end of the track circuit for the block P. At the west end, however, since no such approach relay AT is provided at that end, the code applying relay CPR I0 con-' tinues to be intermittently picked up to transmit a driven code from the west end to the east end of the block P. This driven code will. of course.

pass through the upper winding of the inverse track relay IRI l, thereby causing this relay IE! I. to be picked up. With the relay IRI i once up it is stuck up through its stick circuit including the stick contact I1 and the front contact I8 of the timing relay JR! I. With the inverse track relay IRH at the east end of the block P now energized, and with the corresponding inverse track relay IRH) at the west end deenergized, a driven code is transmitted only from the west end to the east end through the block P. This west-to-east code continues only for its usual three second interval which is then followed by the transmission of a driven code from east to west through the track circuit of the block P. It is thus seen that the approach track relay ATE I at the east end of the block P serves to prevent a code fight, because the code applying relay CPRH has its energizing circuit broken at that time when ordinarily a code fight would take place. That is, the structure is such that one end of a particular block is momentarily rendered incapable of transmitting a driven code as a result of which a driven code is first transmitted from the opposite end of such block and no code fight therefore takes place.

Having thus illustrated several embodiments of the present invention, one of which includes means to prevent a code fight, and having illus trated these embodiments of the invention rather conventionally, it is desired to be understood that the particular embodiments illustrated and the manners in which they have been illustrated have been selected for the purpose of enabling a clear,v

disclosure of the invention to be made and without any intent of illustrating its scope or the specific construction preferably employed in practicing the invention, and it should further be understood that various changes, modifications, and additions may be made to adapt the invention to the particular problem encountered in practicing the same, all without departing; from the spirit or scope of the invention except as demanded by the scope of the appended claims.

What I claim as new is:

1. In a coded track circuit; the combination with a section of track; a driven code transmitter and a track relay at each end of said. section; a selecting means at each end of said section for connecting either said track relay or said driven code transmitter for that end of said section to the track rails; means including timing means at each end of said section erIective after an interval of time to apply an inverse code impulse to said track section immediately after the reception of a driven code impulse and to then actuate said selecting means to substitute the driven code transmitter for said track relay;

and means at each end of said section responsive to an inverse code impulse to actuate the selecting means so as to substitute the track relay for the driven code transmitter.

2. In a coded track circuit for transmitting codes in opposite directions through the rails of a section of railway track alternately, the combination with a section of track divided from the remaining track by insulating joints, a driven code generator at each end of said section for generating a multiple impulse driven code, an inverse impulse generator at each end of said section for generating an inverse impulse during an off period of such driven code transmitted the opposite end of said section, timing means at each end of said section for rendedng said inverse impulse generator effective, code responsive means at each'end of said section, and means at each end of said section responsive to the reception of an inverse impulse to substitute said code responsive means for said driven code generator and also responsive to said timing means to substitute said driven code generator for said code responsive means.

3. In a duplex track circuit including code transmitting and code receiving means for each end of the track section track circuited by such duplex track circuit, a selecting relay at each end of said section which when in its energized position connects its associated code receiving means across the track rails at that end and when in its deenergized position connects its assooiated code transmitting means across the track rails at that end, control means for controlling said selecting relays to cause deenergization of both selecting relays for a particular track section when such track section is occupied and to cause alternate cnergization of said selecting relays so long as such section is unoccupied, each period of energization of said selecting relays being long enough to transmit a multiple element code, and railway signals controlled by said code receiving means.

4. In a duplex track circuit, the combination with a railway track section isolated from adjacent track sections, multiple impulse code creating means including a coding contact at each end of said section, a main track relay and an inverse track relay for each end of said track section, a main track source for each end of said track sections, a selecting relay for each end of said track sections having front contacts included in a circuit including said main track relay and the rails of said section and having back contacts included in series with the rails of said section and in series with two multiple circuits one including a front point of said coding contact and said track source and the other including a back point of said coding contact and said inverse track relay, and control means for controlling said selecting relays to cause deenergization of both selecting relays for said section when said section is occupied and to cause alternate energization of said selecting relays so long as such section is unoccupied, each period of energization of a selecting relay being long enough to transmit a complete multiple element code.

5. In combination with a section of track divided from adjacent track by insulating joints, of a multiple impulse code applying apparatus at each end of said, section, multiple impulse code receiving apparatus at each end of said section,

selecting means at each end of said track section for connecting either the code applying apparatus for transmitting a main code or the code receiving apparatus to the rails at that end of the track section, and control means for controlling said selecting means so that only one of said seleoting means is effective at a time to connect its associated code receiving apparatus to the track rails, each of said control means being controlled by an inverse code element transmitted from the opposite end of the track section and constituting a current impulse transmitted during the off period of the main code then transmitted toward such opposite end of the track section.

6. In combination with a section of track isolated from adjacent track sections, coding means at each end of said section for creating a multiple element code which may be applied to said section and in which the code elements are separated by tim spaces, code responsive apparatus at each end of said section, a selecting relay at each end of said section for when assuming its energized position connecting the associated code responsive apparatus to the track rails and when assuming its deenergized position connecting the associated coding means to the track rails at that end, means effective if a code impulse is received during a time space of a transmitted code received at a particular end and while the selecting relay at such particular end is assuming its deenergized position for picking up such selecting relay and causing that end of thesection to be connected to th associated code responsive means, and code alternating means controlled in part by the code responsive means at the opposite end for transmitting a code impulse during the time space of a transmitted code transmitted from the particular end of said section.

'7. In a duplex track circuit for a track section; the combination with a main track relay, an inverse track relay, an inductive kick relay, a main track source, an inverse track source and a coding contact for each end of said track section; a selecting relay for each end of said track section which when in its energized position connects the main track relay for that end to the rails of said section through a back contact of said inductive kick relay and when in its deenergized position connects the inverse track relay for that end to the track rails through a contact closed when said coding contact is open; a timing relay for each end of said section controlled by the associated selecting relay and effective a predetermined time after such selecting relay has geen energized to inductively connect the associated inductive kick relay to the energizing circuit of its associated main track relay, said inductive kick relay when momentarily assuming its energized position in response to a current impulse induced therein substituting the associated inverse track source for the associated main track relay to transmit an inverse code element to the opposite end of the track section; and a contact on th inverse track relay located at the opposite end of said track section closed in response to such inverse code element and included in the energizing circuit for the selecting relay at such other end of said track section, whereby the actuation of said timing relay at one end of said section results in the operation of the selecting relays at both ends of said track section.

8. In a duplex track circuit; the combination with a track section; a main track relay, an inverse track relay, an inductive kick repeater relay, a coding contact, a track current source and a selecting relay at each end of said track section; a branch circuit for connecting said main track relay to the track rails when its associated selecting relay assumes its energized position and its associated inductive kick repeater relay assumes its retracted position; a second branch circuit for connecting the track current source to the track rails when the associated selecting relay assumes its deenergized position and the associated coding contact is closed; a third branch ci cuit for connecting the inverse track relay to the track rails when the associated selecting relay assumes retracted position and the associated coding contact is open; timing means at each end of said track section which if rendered active causes the transmission of an inverse code element to the opposite end of said track section and then operates its associated selecting relayvto its retracted position; and means controlled by the inverse track relay at such op-- posite end of said section, upon its response to such inverse code element, for actuating its as sociated selecting relay to its energized position.

9. In a coded track circuit; the combination with a section of track, a driven code transmitter, an inverse code transmitter and a track relay at each end of said section; a selecting means at each end of said section for connecting either said track relay or said driven code transmitter for that end of said section to the track rails; timing means at each end of said section effective after an interval of time to apply an inverse code impulse to said track section immediately after th reception of a, driven code impulse and to then actuate said selecting means to substitute the driven code transmitter for said track relay; means at each end of said section responsive to an inverse code impulse to substitute the track relay for the driven code transmitted, and decoding means at each end of said section controlled by the associated track relay. 10. Ina coded track circuit for transmitting codes in opposite directions through the rails of a section of railway track alternately, the combination with a section of track divided from the remaining track by insulating joints, a driven code generator at each end of said section for generating a multiple impulse driven code, an inverse impulse generator at each end of said section for generating an inverse impulse during an off period of such driven code transmitted from the opposite end of said section, timing means at each end of said section for rendering said inverse impulse generator effective, code responsive means at each end of said section, means at each end of said section responsiv to the reception of an inverse impulse to substitute said code responsive means for said driven code generator and also responsive to said timing means to substitute said driven code generator for said code responsive means, and a signal at each end of said section to govern the entrance of trafiic into said section from that end and controlled by the associated code responsive means.

11. In a duplex track circuit including code transmitting and code receiving means for each end of the track section track circuited by such duplex track circuit, a selecting relay at each end of said section which when in its energized position connects its associated code receiving means across the track rails at that end and when in its deenergized position connects its associated code transmitting means across the track rails at that end, control means including an inverse code element transmitting and an inverse code element receiving means for controlling said selecting relays to cause deenergization of both selecting re lays for a particular track section when such rack section is occupied and to cause alternate energization of said selecting relays so long as such section is unoccupied, each period of energization of said selecting relays being long enough to transmit a multiple element code, and railway signals controlled by said code receiving means.

12. In a duplex track circuit, the combination with a railway track section isolated from adjacent track sections, multiple impulse code creating means including a coding contact at each end of said section, a main track relay and "an inverse track relay for each end of said track aei gso m a circuit including saidmam track relay and the iausor said sectionanu navingback' con: -tacts included in series with the rails of said section and in series with two multiple circuits one including a front point ofsaid coding contact and said track source and the other including aback point of said coding contact and said inverse track relay, control means for controlling said selecting relays to cause deenergiz'ation of both selecting relays for said section when said section is occupied and to cause alternate energization of said selecting relays so long as such section is unoccupied, each period of energization of a selecting relay being long enough to transmit a complete multiple element code, and a signal at each end of said track section governing the entrance of trains into said track section and controlled by its associated main track relay.

13. In a duplex track circuit, the combination with a ralway' track section isolated from adjacent track sections, multiple impulse code creating means including a coding contact at each end of said section, amain track relay and aninverse track relay for each end of said track section, a main track source for each end of said track section, a selecting relay for each end of said track section having front contacts included in a circuit including said main track relay and the rails of said section and having back contacts included in series with the rails of said section and in series with two multiple circuits one including a front point of said coding contact and said track source and the other including a back point of said coding contact and said inverse 'track relay, control means for controll'ng said select ng relays to cau e deenergization of both selecting relays for said section when said section isoccupied and to cause alternate energizat on of said selecting relays so long as such section is unoccupiedeach period of energzation of a selecting relay being longenough to transmit a complete multiple element code, decoding means at each end of said track section controlled by its associated main track relay, and a signal at each end of said track section governing themovement of traffic into said section governed by its associated decoding means. v I I 14. In comb nation with a section of track at each end of said section, a selecting relay at each end ofsaid section for when assuming its energized position connecting the associated code responsive apparatus to the track rails and when assuming its deenergized position connecting the associated coding means to the track rails at that end, means effective if a code impulse is received during a time space of a transmitted code received at a particular end and while the selecting relay at such particular end is assuming its deen'erjgi zed position for picking up such selecting relay and causing that end of the section to be connected to the assdciateu code responsive means, code alternating means controlled in part by the code responsive means at the opposite end for transmitting a code impulse during the time each end of said'section, multiple impulse code receiving apparatus ateach end of said section, selecting means at each end of said track section for connecting either thecode applying apparatus for transm tting a main code or the code receiving apparatus to the rails at that end of the track section, control means for controlling said selecting means so that only one of said selecting means is effective at a timeto connect its associated code receiving apparatus to the track rails, each of said control means being controlled by an inverse code element transmtted from the opposite end of the track section and constituting a current impulse transmitted during the off period of the main code then transmitted toward such opposite end of the track section, and signals at each end of said section for governing the movement of trailic into said section and controlled by its associated code receiving apparatus.

15. In combination with a section of track isolated from adiacent track sections, coding means at each end of sa d section for creating a multiple element code which may be applied to said section and in which the code elements are separated by time spaces, code responsive apparatus spacecf a transmitted code transmitted from the particular end of said section, and timing means for controlling said code alternating means.

16. In combination with a section of track isolated from adjacent track section's, coding means at each end of said section for creating a multiple element code which may be applied to said section and in which the c'ode elem'ents are separated by time spaces, code responsive apparatus at eachend of said section, a selecting relay at each end of said section for when assuming its energized position connecting the associated code responsive apparatus to the track rails and when assuming its deenergized position connecting the associated coding means to the track rails at that end, means-effective if a code impulse is received during a time space of a transmitted code received at a' particular end and while the selecting relay at such particular end is assuming its deen'ergiz'ed position for picking up such selecting relay and causing that end of the section to be connected to the associated code responsive means, c'ode alternating mean controlled in part by the code responsive means at the opposite end for transmitting a code impulse during the time space of a transmitted code transmitted from the particular end of said section, timing means forcontrolling' said code alternating means, and signals controlled by said code responsive apparatus. I 7

17. In a duplex track circuit for a track section; the combination with a main track relay, an inverse track relay, an inductive kick relay, a main track source, an inverse track source and a coding contact for each end of said track section; a selecting relay for each end of said track section which when in its energized position connects the main track relay for that end to the rails of said section through a back contact of said inductive kick relay and when in its denergized position connects the inverse track relay for that end tothe track rails through a contact closed when saidcoding contact is open; a timingrelay for eachend of said section controlled by the associated selecting relay and effective a predetermined time after such selecting relayhas been energized to inductively connect the associated inductive kick relay to a winding of its associated main track relay, said inductive kick relay when momentarily assuming its energized position in response to a current impulse induced therein substituting the associated inverse track source for the associated main track relay to transmit an inverse code element to the opposite end of the track section; a contact on the inverse track relay located at the opposite end of said track section closed in response to such inverse code element and included in the energizing circuit for the selecting relay at such other end of said track section, whereby the actuation of said timing relay at one end of said section results in the operation of the selecting relays at both ends of said track section, and signals controlled by said. main track relays.

18. In a duplex track circuit; the combination with a track section; a main track relay, an in- Verse track relay, an inductive kick repeater relay, a coding contact, a track current source and a selecting relay at each end of said track sec tion; a branch circuit for connecting said main track relay to the track rails when its associated selecting relay assumes its energized position and its associated inductive kick repeater relay assumes its retracted position; a second branch circuit for connecting the track current source to the track rails when the associated selecting relay assumes its deenergized position and the associated coding contact is closed; a third branch circuit for connecting the inverse track relay to the track rails when the associated selecting relay assumes retracted position and the associated coding contact is open; timing means at each end of said track section which if rendered active causes the transmission of an inverse code element to the opposite end of said track section and then operates its associated selecting relay to its retracted position; means controlled by the inverse track relay at such opposite end of said section, upon its response to such inverse code element, for actuating its associated selecting relay to its energized position, and signals controlled by said main track relays.

19. In an absolute-permissive-block signaling system; the combination with a single track stretch divided into blocks; a signal at the entrance end of each block for governing the move ment of trafiic into the block from that end; decoding means for each signal; a directional stick relay for each signal including a pick-up circuit closed when a train passes that signal in the direction such signal governs traffic and including a stick circuit closed so long as the block in advance of such signal is occupied; a main code transmitter for each signal controlled in accordance with the condition of occupancy of the block in advance of the block with which it is associated and in accordance with the condition of energization of the directional stick relay associated with the signal governing the movement of traflic in the same direction and into the block next in advance; and means including an inverse code transmitter and an inverse code receiver for alternately rendering the main code transmitter at one end and the decoding means at the other end and the decoding means at said one end and the main cod-e transmitter at said other end efiective.

20. In an absolute-permissive-block signaling system; the combination with a single track stretch divided into blocks; a signal at the entrance end of each block for governing the movement of trafiic into the block from that end; de-

coding means for each signal; a directional stick relay for each signal; a main code transmitter for each signal controlled in accordance with the condition of occupancy of the block in advance of the block with which it is associated and in accordance with the condition of energization of the directional stick relay associated with the signal governing the movement of trafiic in the same direction and into the block next in advance; and means including timing means, an inverse code transmitter and an inverse code receiver for alternately rendering the main code transmitter at one end and the decoding means at the other end effective for a time period and then rendering the decoding means at said one end and the main code transmitter at said other end effective for substantially the same period of time.

21. In combination with a section of track divided from adjacent track by insulating joints, of a multiple impulse code applying apparatus at each end of said section, multiple impulse code receiving apparatus at each end of said section, a selecting relay at each end of said section for when in its deenergized position connecting the code applying apparatus for transmitting a code to the opposite end of said section to the rails of said section and for when in its energized position connecting the code receiving apparatus to the rails of the track section, timing means at each end of said section, and control relays for controlling said selecting relays to their energized and their deenergized positions successively in such manner that only one of said selecting relays is efiective at a time to connect its associated code receiving apparatus to the track rails, each of said control relays being controlled to one position from the opposite end of the track section by the timing means located at such opposite end and being controlled to another position by its associated timing means.

22. In combination with a section of track divided from adjacent track by insulating joints, of a multiple impulse code applying apparatus at each end of said section, multipl impulse code receiving apparatus at each end of said section, selecting means at each end of said section for connecting either the code applying apparatus for transmitting a code to the opposite end of said section or the code receiving apparatus to the rails at that end of the track section, control means at each end of said section having an energized position and a deenergized position for controlling the associated selecting means, timing means at each end of said section for controlling the control means at that end of said section to its deenergized position and controlling the control means at the other end of said section to its energized position substantially simultaneously, and means for controlling each timing means by its associated selecting means.

THOMAS J. JUDGE. 

